2 sticks unsalted butter, plus more for greasing
2 cups sugar
4 large eggs
2 teaspoons vanilla extract
2/3 cup unsweetened cocoa powder
1 cup all-purpose flour
1 teaspoon ground cinnamon
1/4 teaspoon cayenne pepper
1/2 teaspoon salt
1/2 teaspoon baking powder
Preheat the oven to 350 degrees. Line a 9-by-13-inch baking dish with parchment paper, leaving an overhang on two sides. Press the paper into the corners of the pan and lightly grease the paper with butter.
Melt the 2 sticks of butter in a nonstick saucepan over medium-low heat; do not boil. Remove from the heat and let cool slightly. Add the sugar, eggs and vanilla to the saucepan and stir with a wooden spoon until combined.
Add the cocoa, flour, cinnamon, chili powder, salt and baking powder and mix until smooth. Spread the batter in the prepared pan and bake until a toothpick inserted in the middle comes out fudgy, 20 to 25 minutes.
Cool in the pan on a rack, then use the parchment paper to lift out the brownies before slicing.